And if, like me, you are more than familiar with the A9 south of Perth you might have noticed the big yellow poles which were put up two years ago, with roadside CCTV cameras atop them. Most people will be aware that they’re ‘average speed’ cameras; but not that many folk I’ve spoken to know how they work.

As the name suggests, they are designed to record an average of your speed between two points, which is why you see multiple pairs of them on the road. Whenever I travel this road, I see bemused drivers trying weird and wonderful tricks to ‘deal with them’, when they clearly don’t know how they work.

Average speed cameras deploy a device called ANPR, or Automatic Number Plate Recognition. This system is based on the computer in the camera reading the number plates of passing cars, rather than producing the kind of moving footage you might see on Crimewatch. The cameras are carefully positioned to get the best possible picture of a number plate, and nothing else.

The cameras will snap your number plate, regardless of weather conditions and will date and time stamp it before sending it off to a central database. When you pass the next, paired camera, it will take another snap and send it to the same place, where the two will be married up, and a calculation made of how speedily your car passed between the two points.

For simplicity’s sake, let’s say that the two posts are sixty miles apart, in an area speed limited to 60 mph. If you pass the first camera at 1 pm, and the second camera at 2pm, then the system knows you have driven at 60 mph from the distance (60 miles) and the time taken (1 hour). If, however, you pass the second camera at a quarter to two, then the camera knows your speed has averaged 80 mph and a summons, in its ominous brown envelope, will be landing shortly thereafter on your doorstep.

As with any system, there are people convinced they can ‘game’ it by, for instance, driving at 80 mph for the first half hour, stopping for lunch then doing the next half hour at 80 mph again. This might work, but, inevitably, it leaves you open to mobile speed cameras, which will result in your journey being stopped for much longer.

ANPR has come down in price by quite a significant amount over the past few years, and is seeing greater usage outside of busy metropolitan areas. In addition to the traffic calming and speed restrictions, it can monitor traffic flow, or help the police and other law enforcement agencies deny criminals the use of the road network.

So to my fellow travellers on the A9 please be aware that slowing down for the cameras and then speeding up again is going to result in your having a very below average day as well as an above average penalty points tally.